WASHINGTON — Former senator Russ Feingold is giving a boost to Rep. Tammy Baldwin (D-Wis.) in her run for U.S. Senate on Wednesday, encouraging progressives to donate to her to fight back against “Karl Rove, the Koch brothers, and big corporations.”

Feingold will be making his endorsement in an email to Baldwin’s supporters on Wednesday. In the message, he cites her fights in Congress for the middle class and opposition to involvement in Iraq.

“I know Tammy has the values, the vision, and the guts to be a force the middle class in the U.S. Senate,” he writes. “We stood together against going to war in Iraq. And nearly 10 years before the financial collapse, we fought the repeal of the Glass-Steagall Act.”

“These commonsense rules of the road prevented Wall Street and the big banks from making risky investments, and the end of those safeguards led to our economic crisis. Tammy has always put what is right for working Wisconsin families ahead of powerful special interests in Washington.”

In a statement to The Huffington Post, Baldwin said she was “honored to have the support of Russ Feingold, a progressive champion who always puts Wisconsin’s working and middle class families first.”

Baldwin is the only openly gay woman in Congress. If she wins her race in 2012, she will become the first openly gay person to serve in the U.S. Senate.